Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA.
NMR Biomed. 2013 Sep;26(9):1070-8. doi: 10.1002/nbm.2920. Epub 2013 Jan 28.
An MRI method based on the Bloch-Siegert (BS) shift phenomenon was recently proposed as a fast and precise way to map a radio frequency (RF) transmit field (B1(+) field). For MRI at high field, the mapping sensitivity of this approach was limited by tissue heating associated with a BS irradiation pulse. To mitigate this, we investigated the possibility of lowering the off-resonance frequency of this pulse since theoretical analysis indicated that the sensitivity of Bloch-Siegert based B1(+) mapping could be substantially improved when irradiating closer to resonance. Using optimized irradiation pulse shape and gradient crushers to minimize direct excitation effects, in vivo experiments on human brains at 7 T confirmed improved sensitivity with this approach. Improved sensitivity translated into an 80% reduction in B1(+) estimation errors without increasing tissue heating. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.
最近提出了一种基于布洛赫-西格特（Bloch-Siegert，BS）位移现象的 MRI 方法，用于快速准确地绘制射频（RF）发射场（B1(+)场）。对于高场 MRI，该方法的映射灵敏度受到与 BS 辐照脉冲相关的组织加热的限制。为了减轻这种情况，我们研究了降低该脉冲的离频频率的可能性，因为理论分析表明，当辐照更接近共振时，基于 Bloch-Siegert 的 B1(+)映射的灵敏度可以大大提高。使用优化的辐照脉冲形状和梯度破碎机来最小化直接激励效应，在 7T 下对人脑进行的体内实验证实了这种方法的灵敏度提高。灵敏度的提高转化为 B1(+)估计误差减少了 80%，而没有增加组织加热。2013 年发表。本文是美国政府的工作，在美国属于公有领域。
